Oxygen therapy is the administration of oxygen as a therapeutic modality. It is widely used for a variety of purposes in both chronic and acute patient care as it is essential for cell metabolism, and in turn, tissue oxygenation is essential for all physiological functions. Oxygen therapy should be used to benefit the patient by increasing the supply of oxygen to the lungs and thereby increasing the availability of oxygen to the body tissues, especially when the patient is suffering from hypoxia and/or hypoxaemia. Oxygen therapy may be used both in applications in hospital or in home care. The main home care application of oxygen therapy is for patients with severe chronic obstructive pulmonary disease (COPD).
Oxygen may be administered in a number of ways. A preferable way of oxygen administration is by using a so-called on demand generation of oxygen. Referring to this, commercial solutions, so-called oxygen concentrators or separators, respectively, are widely known. These oxygen concentrators mostly separate oxygen from an oxygen containing gas by using a specially designed membrane which preferably is permeable for oxygen but selectively adsorbs other gases, especially nitrogen. Most known oxygen concentrators require a compressor to compress the oxygen containing gas to come up with the demanded oxygen flux of above 1 l/min at atmospheric pressure.
It is widely known to form pure oxygen by using a so called swing process, namely a pressure swing adsorption (PSA) or vacuum swing adsorption (VSA). Swing processes can be typically separated into two steps, namely an adsorption step and a regeneration step. In the adsorption step, mostly a bed with a membrane comprising a physical adsorbent material is contacted with a feed gas mixture of an oxygen containing gas. The oxygen containing gas mostly comprises oxygen and nitrogen. To separate the oxygen from the oxygen containing gas, the physical adsorbent material has sorptive affinity for nitrogen to adsorb this component, while the non adsorbed component (oxygen) forms a flux of pure gas. In order to circumvent saturation of the sorbent material with nitrogen, the latter has to be desorbed from the adsorbent material again. This desorption procedure of the bed, or the membrane, respectively, is the elementary measure of the regeneration step. The regeneration step may be realized by reducing the pressure and/or by flushing the adsorbent with fresh gas, e.g. air.
In a swing process, it is therefore advantageous to provide at least two beds, or membranes, respectively. This allows the different sorptive materials to be operated in an anticyclical manner thereby allowing a constant flow of oxygen containing gas and consequently of formed pure oxygen.
Besides the described PSA and VSA, it is also known to separate gases by applying the so called temperature swing adsorption (TSA). In TSA, heat is supplied to the membrane during the desorption step to improve the latter, whereas no heat is supplied during the adsorption step.
As a further gas separation method, a combined technology has been developed known as TPSA (temperature-pressure swing adsorption). This is a hybrid regeneration cycle, which combines many of the benefits of PSA and TSA whilst minimizing the associated costs. The TPSA process works in a similar manner to TSA, by supplying a heat pulse to drive off impurities from the membrane. However, with TPSA, the heat pulse energy is less than the energy required to desorb all the impurities from the membrane. The remaining impurities are removed by continuing to supply cool regeneration gas after the heat pulse has been extinguished. This second step may be realized because the stream of dry regeneration gas contains heat energy even if it is not heated above its supply temperature. By suitable adjustment of the conditions it is thereby possible to achieve repeated cycles of adsorption and regeneration with only a fraction of the heat of desorption being supplied by heating the regenerating gas.
However, the amount of power consumption is the reason why TSA combined with PSA and/or VSA is not in use for mobile oxygen generators for medical applications.